# AI News, Data Structures Related to Machine Learning Algorithms

- On Thursday, September 6, 2018
- By Read More

## Data Structures Related to Machine Learning Algorithms

So you’ve decided to move beyond canned algorithms and start to code your own machine learning methods.

Maybe you’ve got an idea for a cool new way of clustering data, or maybe you are frustrated by the limitations in your favorite statistical classification package.

Also, because machine learning is a very mathematical field, one should have in mind how data structures can be used to solve mathematical problems and as mathematical objects in their own right.

For data structures classed by operation or abstract data types, it is the opposite: their external appearance and operation is more important than how they are implemented, and in fact they can usually be implemented using a number of different internal representations.

Therefore, the most common types will be the one- and two-dimensional variety, corresponding to vectors and matrices respectively, but you will occasionally encounter three- or four-dimensional arrays either for higher ranked tensors or to group examples of the former.

But the nice thing about these data structures is that, even in more general-purpose programming languages, implementing vectors and matrices is straightforward right next to the metal, assuming the language has any Fortran DNA in it at all.

Consider the translation of matrix-vector multiplication: into C++: In most cases, arrays can be allocated to a fixed size at run time, or you can calculate a reliable upper bound.

As soon as the size of the array exceeds the storage space, a new space is allocated that’s twice the size, the values copied into it, and the old array deleted.

This is an O(n) operation, where n is the size of the array, but since it only happens occasionally, time to add a new value onto the end actually amortizes to constant time, O(1).

For example, to store a sparse matrix: any number of new elements can be added onto the end and they are then sorted by position to make location faster.

If the data is already already sorted, binary trees are less efficient at O(n) worst case since the data will be laid out linearly as if it were a linked list.

While the ordering in a binary tree is constrained, it is by no means unique and the same list can be arranged in many different configurations depending on the order in which it is inserted.

This ordering applies along the hierarchy, but not across it: the parent is always larger than both its children, but a node of higher rank is not necessarily larger than a lower one that’s not directly beneath it.

To take an element off the heap, the larger of the two children is promoted to the missing position, then the larger of those two children is promoted and so on until everything has trickled up the ranks.

So you type in a list of bib numbers of the nearest approaching athletes, then hit a separate key to register the next in the queue as having passed.

Querying the array on “sqrt” would return, “function.” As you work on more problems, you are sure to encounter those for which the standard recipe box does not contain optimal structures.

I mostly use more sophisticated data structures to make the programs a little smoother in how they run and interface with the outside world and a little more user friendly.

Less like the Fortran programs of yore where you had to endure a compile cycle of close to half an hour just to change the grid sizes (I actually worked on a program like this!).

- On Thursday, September 6, 2018
- By Read More

## Querying Arrays with Complex Types and Nested Structures

Examples in this section show how to change element's data type, locate elements within

This query returns: To change the field name in an array that contains ROW values, you can CAST the ROW declaration:

This query returns: In the following example, select the accountId field from the userIdentity column of a AWS CloudTrail logs table by using the dot .

This query returns: To query an array of values, issue this query: It returns this result: Large arrays often contain nested structures, and you need to be able to filter, or

To define a dataset for an array of values that includes a nested BOOLEAN value, issue this query:

This query selects the nested fields and returns this result: To filter an array that includes a nested structure by one of its child elements,

takes as an input a regular expression pattern to evaluate, or a list of terms separated

pipe (|), evaluates the pattern, and determines if the specified string contains it.

- On Thursday, September 6, 2018
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## Data Structures and Algorithms/Arrays, Lists and Vectors

If you have taken the prerequisites to this course or have done any more than the very basics of programming you will have come across arrays.

The elements in the array must all be shifted up one index after the insertion, or all the elements must be copied to a new array big enough to hold the inserted element.

However, the linked list requires linear O(N) time to find or access a node, because there is no simple formula as listed above for the array to give the memory location of the node.

If nodes are to be inserted at the beginning or end of a linked list, the time is O(1), since references or pointers, depending on the language, can be maintained to the head and tail nodes.

Importantly, linked lists tend to suffer from severe slowdown due to CPU cache misses during traversal, caused by nodes being stored in a non-contiguous fashion.

This slowdown is mostly absent when nodes are stored in contiguous memory (as is normal when they are initialized) but worsens when nodes are stored apart from each other (which commonly occurs as more nodes are added later on).

This slowdown is often enough to warrant the use of another data structure, although linked lists may still be preferred in cases where data is inserted/deleted frequently and the list is traversed sparingly.

In order to do this efficiently, the typical vector implementation grows by doubling its allocated space (rather than incrementing it) and often has more space allocated to it at any one time than it needs.

- On Thursday, September 6, 2018
- By Read More

## 'predict()' should marshal return values into nicer data structures when appropriate #49

array([ 1.37737417], dtype=float32)}, {'predictions': array([ 1.63807189], dtype=float32)}, {'predictions': array([ 1.71594262], dtype=float32)}, {'predictions': array([ 1.66177177], dtype=float32)}, {'predictions': array([ 1.37737417], dtype=float32)}, {'predictions': array([ 1.42138815], dtype=float32)}, {'predictions': array([ 1.37398851], dtype=float32)}, {'predictions': array([ 1.56020117], dtype=float32)}, {'predictions': array([ 1.76334214], dtype=float32)}, {'predictions': array([ 1.65500033], dtype=float32)}, {'predictions': array([ 1.76334214], dtype=float32)}, {'predictions': array([ 1.37398851], dtype=float32)}, {'predictions': array([ 1.32658899], dtype=float32)}, {'predictions': array([ 1.53311574], dtype=float32)}, {'predictions': array([ 2.00372577], dtype=float32)}, {'predictions': array([ 1.72609973], dtype=float32)}, {'predictions': array([ 1.40107405], dtype=float32)}, {'predictions': array([ 1.37398851], dtype=float32)}, {'predictions': array([ 1.26903236], dtype=float32)}, {'predictions': array([ 1.61098647], dtype=float32)}, {'predictions': array([ 1.5974437], dtype=float32)}, {'predictions': array([ 1.58390105], dtype=float32)}, {'predictions': array([ 1.66177177], dtype=float32)}, {'predictions': array([ 1.35028875], dtype=float32)}, {'predictions': array([ 1.42815948], dtype=float32)}, {'predictions': array([ 1.40107405], dtype=float32)}, {'predictions': array([ 1.66177177], dtype=float32)}, {'predictions': array([ 1.65500033], dtype=float32)}, {'predictions': array([ 1.58728671], dtype=float32)}, {'predictions': array([ 1.71594262], dtype=float32)}, {'predictions': array([ 1.83444154], dtype=float32)}, {'predictions': array([ 1.26903236], dtype=float32)}] That is, the generator literally returns a whole bunch of dictionaries of length-one arrays.

- On Thursday, September 6, 2018
- By Read More

## ArrayList. Data structures in pictures.

If the constructor is called without parameters, then by default an array of 10 elements of type Object (with reduction to the type, of course) will be created.

Below is shown a cycle that alternately adds 15 elements: When adding the eleventh element, the check shows that there are no places in the array.

As you might guess, when there is an insertion of an element by index and there are no empty spaces in your array, the call to System.arraycopy() happens twice: the first in ensureCapacity(), the second in the method add (index, value), which will clearly affect the speed of the entire operation of the addition.

You can delete items in two ways:- by the index remove(index)- by the value of remove(value) With the removal of the element on the index, everything is simple enough int numMoved = size - index - 1;

- On Tuesday, January 22, 2019

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